Keep BackEffect of rotation animation for visible wallpaper

Even if the enter animation doesn't set alpha, if the entering content
has a non-opaque layer, e.g. wallpaper, it may be flickering at the
end of animation because the non-opaque layer will be blended with the BackColorSurface layer.

Bug: 438615184
Flag: com.android.window.flags.no_alpha_rotation_enter_animation
Test: Rotate when wallpaper is visible with light color.
Change-Id: I19366ba94511458dbce99109e8fd82409d568725